On open channel flow is the flow of liquids in a channel whose geometry is such that one liquid surface is free of solid boundaries. Typically, such flows occur in channels, pipes, that are not flowing full, pools, tanks, or the like. In industrial applications, open channel flows are encountered in form of process effluent streams in thermal exchange as well as removal/delivery applications.
Traditionally, emersion pumps have been utilized for pumping liquid from a lower level (lower pressure) to a relatively higher level (higher pressure). However, an open channel flow is subject to air entrainment due to secondary circulation and, particularly in cases where the specific flow channel functions as a manifold for receiving several partial or side flows. Air entrained in the open channel flow is thus present as free and combined air, which collectively tends to cause substantial pumping problems because the presence of air or gas in the pumped liquid or suspension rapidly leads to pump cavitation, i.e. the combination of air released and vaporization caused by low pressure induced in the liquid, as well as to disturbances of subsequent processes to which the liquid or suspension containing the entrained air is directed. Apparent disadvantages of a pump immersed into an open channel flow include the tendency of the pump to become clogged by solid or semi-solid matter, as well as problems associated with the maintenance of such pumps.
It is thus an object of the present invention to overcome the above mentioned disadvantages and to provide an arrangement or system for pumping liquids from flows at negative static head, i.e. the pumping apparatus is located above the free surface of the liquid supply.